If it's telling you you need to use navigateToURL, you are using Actionscript 3. In AS3, to make a button/movieclip work with code, you need to add an event listener and event handler function for it. You might need to add a few (for different events, like rollover, rollout, clicking it, but for now we'll just say you want to be able to click it to get a web page to open. In the timeline that holds that button, in a separate actions layer that you create, in a frame numbered the same as where that button exists, you would add the event listener:

btn1.addEventListener(MouseEvent.CLICK, btn1Click);

The name of the unique function for processing the clicking of that button is specified at the end of the event listener assignment, so now you just have to write that function out: